Linolenic acid (18:3-omega 3) is the most common fatty acid in the class of polyunsaturated fatty acids known as omega-3 fatty acids. While there is no consistent clinical data as to whether omega-3 fatty acids are a dietary essential for human infants, it is known that human milk does contain linolenic acid. Dietary deprivation of omega-3 fatty acids in growing rats and primates has been associated with visual impairment. Dietary omega-3 fatty acids may also be essential for normal prenatal and postnatal development of the retina and brain.
Linolenic acid is present in soybean, canola, and linseed oils. Attempts have been made to formulate spray dried products containing soy oil to provide linolenic acid with limited success. Exposure of the unsaturated fatty acids to heat and oxygen in the presence of catalysts like iron and copper during the spray drying process has resulted in powdered nutritional products with unacceptable sensory attributes resulting from oxidative rancidity. Oxidation reactions occur when electrons are removed from an atom or group of atoms, when oxygen is added to carboncarbon double bonds and a corresponding reduction reaction that involves the addition of electrons to an atom or group of atoms. Oxidation reactions involving unsaturated lipids result in the development of undesirable flavors and odors. In food systems, antioxidants function by being preferentially oxidized or by interrupting the freeradical chain mechanism.
Optimization of the oil blend in powdered infant formulas will result in products with fatty acid profiles which are similar to the corresponding liquid infant formulas and also closer to that of human milk. The level of oleic acid will also be optimized. Oleic acid concentrations in current formulations are considerably less than that found in human milk. Oleic acid is a precursor of C24:1, which is essential for myelination and nervous system development. The increased level of mono-unsaturated oleic acid may exhibit a protective effect on the oxidation of the more unsaturated fatty acids such as linolenic acid. Oleic acid may act as free radical scavenger and block propagation of linolenic acid oxidation.
U.S. Pat. 3,950,266 teaches antioxidant compositions of rosemary or sage which have been extracted using a particular procedure. The antioxidant property of the extract may be enhanced by the addition of ascorbic acid or citric acid. The antioxidant compositions are claimed to have utility with soybean oil, and are especially useful when the oil is subjected to elevated temperatures, as in the case of deep frying foods. There is no indication in this patent that the antioxidant compositions may have utility in a powdered food product.
U.S. Pat. No. 5,077,069 teaches a natural antioxidant system comprising tocopherols, ascorbic acid, citric acid and phospholipids. Rosemary extract may optionally be employed in this antioxidant system. The tocopherols may be supplied by a vegetable oil, such as soybean oil. The patent teaches that citric acid does not have a strong effect on antioxidant activity in fish oil, but is important in the prevention of the development of an off-color. This patent teaches that the use of ascorbyl palmitate as an antioxidant in oil is not desirable. This patent contains only examples of the use of the antioxidant system with liquid oils and not with a powdered product.
U.S. Pat. No. 4,692,340 relates to a method of improving the "keeping quality" of a powdered pediatric nutritional product by producing a sugar film around the fat in the product. The fat system suggested in this patent comprises milk fat (preferably clarified butter), vegetable fat (preferably sunflower seed oil) and lard. While this system is much different from the antioxidant blend disclosed herein, it does serve to point out that the necessity to prevent oxidation of fat sources in powdered nutritional products has been recognized as a problem for quite sometime.
Published Japanese Patent Application Hei 2-55785 (published 1990) describes an antioxidant system for storage of oils (in the liquid state) containing tocopherols, ascorbic acid, ester, and tea extracts.
Substantial development work has resulted in the successful formulation of liquid infant formulas with a modified lipid blend containing optimized levels of omega-3 fatty acids. An oil blend has been identified which provides desirable levels of oleic, linoleic, and linolneic acids in powdered infant formulas. This blend contains 28% soy oil, 42% high oleic safflower oil, and 30% coconut oil. Incorporation of polyunsaturated fatty acids into spray dried nutritional products presented the technical challenge of protecting the products from oxidation which in the past has resulted in undesirable rancidity when exposing these unsaturated oils to the heat and air involved in spray drying. In order to minimize rancidity resulting from oxidation of the unsaturated fatty acids, combinations of natural antioxidants and a chelating agent may be incorporated into a product in accordance with the present invention. Levels oflinolenic acid, linoleic acid, oleic acid and long chain omega-3 fatty acids in infant formula powders may be optimized using oil blends containing combinations of soy, canola, high oleic safflower, corn, coconut, and marine oils.